Friction welding process

ABSTRACT

A friction welding process comprises providing a first workpiece ( 10 ) having a first weld surface ( 16 ), and a second workpiece ( 12 ) having a second weld surface ( 18 ). The first and second workpieces ( 10, 12 ) can be welded together at the first and second weld surfaces ( 16, 18 ). The workpieces ( 10, 12 ) are arranged in engagement with each other at the weld surfaces ( 16, 18 ). Relative oscillatory motion is affected to the workpieces ( 10, 12 ) such that at least one weld surface moves across the other, thereby raising the temperature at the weld surfaces ( 16, 18 ) to create a weld interface. The relative oscillatory motion is ceased and the weld surfaces ( 16, 18 ) are allowed to cool to weld the first and second workpieces ( 10, 12 ) together at the interface. The first workpiece ( 10 ) has an outwardly extending portion ( 15 ), and the first weld surface ( 16 ) is provided on the outwardly extending portion ( 15 ). The outwardly extending portion ( 15 ) includes an apex region ( 14 ), which engages the second weld surface ( 18 ). A side face ( 20 ) extends from one side of the apex region ( 14 ) to provide a gap between the side face ( 20 ) and the second weld surface ( 18 ). The aforementioned gap being of sufficient size to allow weld flash material formed during said oscillatory motion to pass from the weld interface through said gap.

This invention relates to friction welding processes.

Linear friction welding is the process for welding together two bodiesor workpieces by converting mechanical energy to heat energy by thefriction between the engaging weld surfaces of the two workpieces. Theprocess involves effecting relative linear motion between the twoworkpieces while the weld surfaces remain in engagement with each other.

Linear friction welding in a normal atmosphere results in the formationof atmospheric reaction products due to the high temperatures.Additionally, surface contamination of the weld interfaces can also giverise to weld anomalies. Due to the flow regimes of the flash materialbetween the two workpieces during the reciprocating motion of linearfriction welding, the weld contamination may not be expelled from theweld zone by the flash material flow. At high levels of weldcontamination, there may be a reduction in weld strength and life andcause the welded product to fail the quality standards required by highintegrity joints.

According to one aspect of this invention, there is provided a frictionwelding process comprising providing a first workpiece comprising afirst weld zone having a first weld surface and a second workpiececomprising a second weld zone having a second weld surface, at whichweld surfaces the workpieces can be welded together, arranging theworkpieces in engagement with each other at said weld surfaces,effecting oscillatory motion of the workpieces relative to each othersuch that at least one weld surface moves across the other, therebyraising the temperature at said weld surfaces to create a weldinterface, and ceasing said relative oscillatory motion and allowing theweld surfaces to cool to weld the first and second workpieces togetherat said interface, wherein the first weld zone has an outwardlyextending portion and the first weld surface is provided on theoutwardly extending portion, the outwardly extending portion includes anapex region to engage the second weld surface and has a side faceextending from one side of the apex region to provide a gap between theside face and the second weld surface, the aforementioned gap being ofsufficient size to allow weld flash material formed during saidoscillatory motion to pass from the weld interface through said gap.

According to another aspect of this invention, there is provided aworkpiece for use in a friction welding process, the workpiececomprising a weld zone having a weld surface for engagement with acorresponding weld surface on a body, and the weld zone furthercomprising an outwardly extending portion, wherein the weld surface isprovided on the outwardly extending portion, the outwardly extendingportion includes an apex region to engage the second weld surface on thebody and has a side face extending from one side of the apex region toprovide a gap between the side face and the second weld surface, theaforementioned gap being of sufficient size to allow weld flash materialformed during the friction welding process to pass therethrough.

The first and second weld surfaces may be generally planar.Alternatively, the first and second weld surfaces may be curvilinear.

The weld surfaces may be elongate. The direction of said motion may betransverse to the first weld surface. Alternatively, the direction ofsaid motion may be along the first weld surface.

Conveniently, the outwardly extending portion is a tapering portion. Inone embodiment, the tapering portion may be partially or wholly consumedduring the welding process.

Preferably, the relative oscillating motion is linear motion. Themaximum amplitude of oscillation is preferably half the width of thefirst weld surface plus half the width of the second weld surfaces. Forthis purpose, the amplitude of oscillation is defined as being themaximum displacement from the centre of oscillation.

In one embodiment, the outwardly extending portion may have generallystraight sides, and may be of a generally pyramidal configuration.Alternatively, the outwardly extending portion may be of a domed convexconfiguration.

In the preferred embodiment of the present invention the outwardlyextending portion comprises a further side face extending from theopposite side of the apex region to the first mentioned side face. Theside faces may be generally symmetrical to each other about a centralaxis or plane of outwardly extending portion.

The apex region may be generally curvilinear. In one embodiment, theapex region may initially have a width of no more than substantially 5mm, preferably no more than substantially 1 mm. The further side facemay taper relative to the apex region.

The, or each side face may taper from the apex region at an angle in therange of 6° to 12°, conveniently substantially 8°.

Preferably, the size of the gap is greater than the thickness of theweld flash material. Where the gap is formed by the, or each, tapersidewall, the angle of the, or each, side face to the second weldsurface is preferably greater than the angle subtended to the weldinterface by the thickness of the weld flash material.

In some embodiments, the weld flash material may form successive regionsof greater or lesser thickness. Preferably, the angle of the, or each,side face to the second weld surface is greater than the angle subtendedat the weld interface by the region of greater thickness of the weldflash material closest to the weld interface.

Preferably, the apex region has a dimension extending generallytransverse to the direction of motion. Preferably, the side faces tapergenerally along the direction of motion.

In the preferred embodiment, the outwardly extending portion providesthe advantage, that the flow regime of the weld flash during the weldingprocess is different to the flow regime when the weld surfaces aregenerally parallel. In the preferred embodiment, a central weld zone iscreated between the two surfaces and the flow regime created with theoutwardly extending portion aids the expulsion of weld anomalies fromthe central weld zone. Also, in the preferred embodiment, the outwardlyextending portion acts to expel weld anomalies which are either presenton the surfaces or which form in regions of the surface open to theatmosphere.

The preferred embodiment of this invention provides the advantage thatan upstanding tapering region at the weld interface which expels defectsfrom the interface by changing the flow regime from that which would beexpected by the use of planar surfaces.

Embodiments of the invention will now be described by way of exampleonly, with reference to the accompanying drawings, in which:—

FIG. 1A is an end view of first and second workpieces undergoing afriction welding process;

FIG. 1B is a plan view of the first workpiece shown in FIG. 1A;

FIG. 2 is a side view of a curvilinear weld plane between first andsecond workpieces;

FIG. 3 is a perspective view of the first and second workpieces shown inFIG. 2;

FIG. 4 is a plan view of a part of the first workpiece shown in FIG. 2;and

FIG. 5 is a perspective view of a blade being applied to a blisk.

Referring to FIG. 1A, there is shown first and second workpieces 10, 12undergoing a linear friction welding process. The first and secondworkpieces 10, 12 can be any suitable bodies formed of a material, whichis suitable for welding by a friction welding process such as linearfriction welding. In particular, in the embodiment the first and secondworkpieces 10, 12 are respectively a disc and a rim post to be used inmanufacturing a turbine disc. The first workpiece 10 comprises a weldzone 11 having an outwardly extending portion in the form of anupstanding tapering portion 14 having provided thereon a first weldsurface 16. The first weld surface 16 is, in the embodiment shown,elongate and has a width of substantially 1 mm. The tapering portion 14has a centreline 17 (see FIG. 1B).

The first workpiece 10 is shown in plan view in FIG. 1B and includes aprojecting part 15 from which the tapering portion 14 extends. The weldsurface 16 is an apex region of the tapering portion 14, and isgenerally planar in configuration. The weld surface 16 substantiallyfollows the centreline 17.

The second workpiece 12 comprises a second weld surface 18, whichcomprises a second weld zone 19.

The first and second weld zones 11, 19 on the respective first andsecond workpieces 10, 12 are the zones of the two workpieces at whichthey are welded together, as described below.

The tapering portion 14 comprises first and second opposite taperingside faces 20, 22 which extend outwardly from the weld surface 16 whichis also the apex of the tapering portion 14. In addition, the taperingportion 14 comprises first and second end faces 24, 26 that aregenerally perpendicular to the weld surface 16 from the opposite ends ofthe weld surface 16 of the tapering portion 14. The side faces 20, 22extend from the weld surface 16 at an angle α in the region of between6° and 12°.

In the embodiment shown in FIGS. 1A and 1B, the first and secondworkpieces 10, 12 are in the form of components prior to machining. Ineach case the broken lines 23 represent the configuration of the finalproduct.

It will be appreciated, however, that if desired, the first and secondworkpieces 10, 12 could be in the form of the final products, which havealready been machined.

FIGS. 2, 3 and 4 show a further embodiment, which comprises many of thefeatures shown in FIGS. 1A and 1B. These features have been designatedwith the same reference numerals.

The embodiment shown in FIGS. 2, 3 and 4 differs from that shown inFIGS. 1A and 1B in that the embodiment shown in FIGS. 2, 3 and 4 hascurvilinear weld surfaces 16, 18. As a result, the direction of relativemovement of the workpieces is generally transverse to the centre line 17of the weld surface 16 (see FIG. 4). The direction of said relativemovement is shown by the double arrow B shown in FIGS. 3 and 4.

In operation, the first and second weld zones 11, 19 are brought intoengagement with each other, and relative linear motion is effectedbetween the first and second workpieces 10, 12, in the direction asshown by the double headed arrow A in FIGS. 1, 3 and 4.

By effecting this linear motion and normal force, in a manner whichwould be immediately apparent to the person skilled in the art, thefrictional heat which is created at the interface between the first andsecond weld surfaces 16, 18, causes the temperature at the first andsecond weld surfaces 16, 18 to rise to values approaching, but below,the melting range of the respective materials on which the first andsecond workpieces 10, 12 are formed. The relative motion of the twoworkpieces 10, 12 wears away the tapering portion 14, thereby increasingthe width of the first surface 16. When the tapering portion 14 has beenfully, or partially, worn away, as determined by the person skilled inthe art, the relative movement is then stopped and the pressure appliedto the first and second workpieces 10, 12 causes the two bodies to bewelded together as the interface between the first and second weldsurfaces 16, 18 cools.

During the relative movement of the first and second bodies, a flow ofweld flash is established in which, due to the taper of the side faces20, 22, and of the end faces 24, 26 the weld flash is extruded from theweld interface between the first and second weld surfaces 16, 18. Inaddition, any defects, for example in the form of atmospheric reactionproducts formed due to the high temperatures are also expelled from theweld interface during the welding stage. A tapering gap is formedbetween the side faces 20, 22, and the second weld surface 18. Thetapering gap so formed allows expulsion of weld defects as they arecreated in areas open to the atmosphere.

FIG. 5 shows an embodiment in which a turbine blade 40 is weldeddirectly to the upstanding tapering portion 14 on a disc 42. The turbineblade 40 has a base member 44 which constitutes the second workpiece 12.The disc 42 has a plurality of radially outwardly extending stubs 46which constitute the first workpiece 10.

In order to weld the base member 44 of the blade 40 to the stub 46 onthe disc 42, the respective weld surfaces 16, 18 are brought intoengagement with each other and relative linear motion is effected to thetwo bodies in the directions of the double headed arrow B, in the sameway as described above to weld the two components together.

Thus, the above-described embodiment provides the advantage of allowingthe welding together of two workpieces at a weld interface, which isgenerally free from weld anomalies.

Various modifications can be made without departing from the scope ofthe invention. For example, the end faces 26, 24 could taper relative tothe first weld surface 16. Also, the workpieces 10, 12 could be formedof other materials which could be welded by friction welding, forexample, plastics materials. A further modification is that the secondworkpiece 12 could comprise an outwardly extending portion in the formof an upstanding tapering portion, as shown by the broken lines 30. Theupstanding tapering portion 30 could have all the features of theaforementioned upstanding tapering portion 14 as described above. Theupstanding tapering portion 30 defines a weld surface 32, as shown inFIG. 1. Another modification is that the side faces 20, 22 could becurved.

1. A friction welding process comprising the steps of providing a firstworkpiece comprising a first weld zone having a first weld surface and asecond workpiece comprising a second weld zone having a second weldsurface, at which weld zones the workpieces can be welded together,arranging the workpieces in engagement with each other at said weldsurfaces, effecting oscillatory motion of the workpieces relative toeach other such that at least one weld surface moves across the other,thereby raising the temperature at said weld surfaces to create a weldinterface, and ceasing said relative oscillatory motion and allowing theweld surfaces to cool to weld the first and second workpieces togetherat said interface, wherein the first weld zone has an outwardlyextending portion and the first weld surface is provided on theoutwardly extending portion, the outwardly extending portion includes anapex region to engage the second weld surface and has a side faceextending from one side of the apex region to provide a gap between theside face and the second weld surface, the aforementioned gap being ofsufficient size to allow weld flash material formed during saidoscillatory motion to pass from the weld interface through said gap. 2.A friction welding process according to claim 1 in which the outwardlyextending portion is a tapering portion and the side face tapersrelative to the apex region.
 3. A friction welding process as claimed inclaim 1 in which the outwardly extending portion comprises a second sideface extending from the opposite side of the apex region to the firstmentioned side face.
 4. A friction welding process as claimed in claim 3in which the second side face tapers relative to the apex region.
 5. Afriction welding process according to claim 4 in which the outwardlyextending portion has a generally triangular profile.
 6. A frictionwelding process according to claim 4 in which the outwardly extendingportion has a curved configuration.
 7. A friction welding processaccording to claim 1 in which one or both of the side faces taperrelative to the second weld surface and the gap is formed by the taperof one or both of the side faces, and one or both of the side faces hasan angle relative to the second weld surface which is greater than theangle subtended at the weld interface by the thickness of the weld flashmaterial.
 8. A friction welding process according to claim 1, whereinthe weld flash material expelled from the weld interface into the gapforms successive regions of greater and lesser thickness, the angle ofone or both side faces to the second weld surface is greater than theangle subtended at the weld interface by the region of greater thicknessof the weld flash material closest to the weld interface.
 9. A frictionwelding process according to claim 1 wherein one or both side facestapers relative to the apex region at an angle of between substantially6° and substantially 12°.
 10. A friction welding process according toclaim 1, wherein one or both of the side faces taper relative to theapex region at an angle of substantially 8°.
 11. A friction weldingprocess according to claim 1 wherein the apex region has a dimensionextending generally transverse to the direction of oscillating motion,and the side faces taper generally along, or transverse to, thedirection of oscillating motion.
 12. A friction welding processaccording to claim 1, wherein the relative oscillating motion of thefirst and second workpieces is a linear motion.
 13. A friction weldingprocess according to claim 1, wherein the maximum amplitude ofoscillation is half the width of the first weld surface plus half thewidth of the second weld surface, where the oscillation amplitude is themaximum displacement from the centre of oscillation.
 14. A frictionwelding process according to claim 1 in which the first and second weldsurfaces are curvilinear.
 15. A friction welding process according toclaim 1 in which the first weld surface is elongate, and the directionof said motion is transverse to the first weld surface.
 16. A frictionwelding process according to claim 1 in which the first weld surface iselongate and the direction of said motion is generally along the firstweld surface.
 17. A friction welding process according to claim 1 inwhich the second workpiece has an outwardly extending portion and thesecond weld surface is provided on the outwardly extending portion ofthe second workpiece.
 18. A workpiece for use in a friction weldingprocess, the workpiece comprising a first weld surface for engagementwith a corresponding second weld surface on a further body, theworkpiece further comprising an outwardly extending portion, wherein thefirst weld surface is provided on the outwardly extending portion, theoutwardly extending portion includes an apex region to engage the secondweld surface on the further body and has a side face extending from oneside of the apex region to provide a gap between the side face and thesecond weld surface, the aforementioned gap being of sufficient size toallow weld flash material formed during the friction welding process topass therethrough.
 19. A workpiece as claimed in claim 18 in which theside face tapers relative to the apex region.
 20. A workpiece accordingto claim 18 in which the outwardly extending portion comprises a secondside face extending from the opposite side of the apex region to thefirst mentioned side face.
 21. A workpiece according to claim 20 inwhich the side faces are generally symmetrical to each other about acentral axis or plane of outwardly extending portion
 22. A workpieceaccording to claim 18 in which the second side face tapers relative tothe apex region.
 23. A workpiece according to claim 18 in which theoutwardly extending portion has a triangular profile.
 24. A workpieceaccording to claim 18 in which the outwardly extending portion has acurved configuration.
 25. A workpiece according to claim 18, whereineach side face tapers relative to the weld surface of the body and thegap is formed by the taper of each side face, and each side face has anangle relative to the weld surface of the body which is greater than theangle subtended at the weld interface by the thickness of the weld flashmaterial.
 26. A workpiece according to claim 25, wherein where the weldflash material expelled from the weld interface into the gap formssuccessive regions of greater and lesser thickness, the angle of theside face to the weld surface of the body is greater than the anglesubtended at the weld interface by the region of greater thickness ofthe weld flash material closest to the weld interface.
 27. A workpieceaccording to claim 18 in which one or both side faces tapers relative tothe apex region at an angle of between 60 and substantially
 120. 28. Aworkpiece according to claim 18, in which the one or both side facestaper relative to the apex region at an angle of substantially 8°.
 29. Aworkpiece according to claim 18 wherein the first weld surface isgenerally planar.
 30. A workpiece according to claim 18 wherein thefirst weld surface is curvilinear.
 31. A workpiece according to claim 18wherein the apex region has a dimension extending generally transverseto the direction of linear motion, and the side face taper generallyalong the direction of linear motion.